1. Field of the Invention
The present invention relates to a metallizing apparatus, and more particularly to an apparatus in which a metal is vacuum deposited on a surface which is intended to be a signal surface of an optical disk, such as a digital audio disk, a video disk or the like, to form a reflecting film thereon.
2. Prior Art
FIGS. 5-8 show a conventional metallizing apparatus.
Referring to FIG. 5 a housing 2 defines an evaporation chamber which provides a metal evaporation environment in a vacuum and within which a circular base 1 is placed.
On the base 1 are provided a plurality of rotary shafts 3 in equally spaced relation around the circular base. Each of the shafts 3 is provided with a plate-like disk holder 6 for holding an optical disk 5 to be metallized. A drive means, though not shown, is provided for driving the base 1 into rotation together with the respective rotary shafts 3.
As shown in FIG. 6, a pair of electrical feeding rods 8 serving as an electrode, is provided such that the rods are in parallel to each other in the middle of the base 1. A plurality of filaments 10, which carry a metal, such as Al, to be deposited onto the optical disk substrate, are arrayed in parallel between the feeding rods. Each of the filaments 10 has a voltage applied thereto from a power supply 11 through the feeding rods 8 by an ON/OFF switch 12.
FIGS. 7 and 8 illustrate means for securing the ends of the filaments 10 to the feeding rods 8.
As shown in the figures, the securing means is formed of a supporting member 15 and a depressing bolt 16. The supporting member 15 has a recess portion 15a facing the electrical feeding rod 8 and is secured to the electrical feeding rod 8 by means of a bolt 14 passing therethrough. A depressing bolt 16 depresses the filament 10, passing through the recess 15a, against the electrical feeding rod 8.
With the aforementioned prior art metallizing apparatus, the filament 10 is in contact with the electrical feeding rod 8 through only the area of a "spot" portion at which the filament is depressed against the electrical feeding rod 8 by means of the depressing bolt 16. This can result in a poor contact between the electrical feeding rod 8 and the filament 10, which leads to the problem that the metal vapor of sufficient density cannot be obtained and thus the reflecting film deposited on the optical disk substrates 5 is not of uniform thickness. Non-uniform thickness of the reflecting film causes the reflectivity of the thus produced optical disk to be less than a predetermined level. This problem needs to be solved to improve yield.
As shown in FIG. 8, since the tip end portion of the depressing bolt 16 is exposed at the recess portion 15a on the supporting member 15, the metal vapor can be deposited on the threaded portion which is exposed, causing difficulty in unscrewing the depressing bolt when replacing the filament 10.
Further, in the aforementioned arrangement, the depressing bolt must be rotated many times to secure the filament to the feeding rod or to disconnect from the feeding rod, and therefore the replacement of the filament is a rather time-consuming job and is a nuisance to the workman. Also the prior art suffers from the problem that, as shown in FIG. 8, the filament 10 may easily slip off the bolt 16 when the depressing bolt 16 is rotated. As a result it is difficult to secure the filament in position.